The ever-expanding role of cytokine receptor DR3 in T cells.

Death Receptor 3 (DR3) is a cytokine receptor of the Tumor Necrosis Factor receptor superfamily that plays a multifaceted role in both innate and adaptive immunity. Based on the death domain motif in its cytosolic tail, DR3 had been proposed and functionally affirmed as a trigger of apoptosis. Further studies, however, also revealed roles of DR3 in other cellular pathways, including inflammation, survival, and proliferation. DR3 is expressed in various cell types, including T cells, B cells, innate lymphocytes, myeloid cells, fibroblasts, and even outside the immune system. Because DR3 is mainly expressed on T cells, DR3-mediated immune perturbations leading to autoimmunity and other diseases were mostly attributed to DR3 activation of T cells. However, which T cell subset and what T effector functions are controlled by DR3 to drive these processes remain incompletely understood. DR3 engagement was previously found to alter CD4 T helper subset differentiation, expand the Foxp3+ Treg cell pool, and maintain intraepithelial γδ T cells in the gut. Recent studies further unveiled a previously unacknowledged aspect of DR3 in regulating innate-like invariant NKT (iNKT) cell activation, expanding the scope of DR3-mediated immunity in T lineage cells. Importantly, in the context of iNKT cells, DR3 ligation exerted costimulatory effects in agonistic TCR signaling, unveiling a new regulatory framework in T cell activation and proliferation. The current review is aimed at summarizing such recent findings on the role of DR3 on conventional T cells and innate-like T cells and discussing them in the context of immunopathogenesis.

Proinflammatory IFNγ Is Produced by but Not Required for the Generation of Eomes+ Thymic Innate CD8 T Cells.

Innate CD8 T cells are proinflammatory effector T cells that achieve functional maturation in the thymus prior to their export into and maturation in peripheral tissues. Innate CD8 T cells produce the Th1 cytokine IFNγ but depend on the Th2 cytokine IL-4 for their generation. Thus, innate CD8 T cells can permute the intrathymic cytokine milieu by consuming a Th2 cytokine but driving a Th1 cytokine response. The cellular source of IL-4 is the NKT2 subset of invariant NKT (iNKT) cells. Consequently, NKT2 deficiency results in the lack of innate CD8 T cells. Whether NKT2 is the only iNKT subset and whether IL-4 is the only cytokine required for innate CD8 T cell generation, however, remains unclear. Here, we employed a mouse model of NKT1 deficiency, which is achieved by overexpression of the cytokine receptor IL-2Rß, and assessed the role of other iNKT subsets and cytokines in innate CD8 T cell differentiation. Because IL-2Rß-transgenic mice failed to generate both NKT1 and innate CD8 T cells, we postulated an in vivo requirement for IFNγ-producing NKT1 cells for innate CD8 T cell development. In-depth analyses of IL-2Rß-transgenic mice and IFNγ-deficient mice, however, demonstrated that neither NKT1 nor IFNγ was required to induce Eomes or to drive innate CD8 T cell generation. Instead, in vivo administration of recombinant IL-4 sufficed to restore the development of innate CD8 T cells in NKT1-deficient mice, affirming that intrathymic IL-4, and not IFNγ, is the limiting factor and key regulator of innate CD8 T cell generation in the thymus.

Markers and makers of NKT17 cells.

Invariant natural killer T (iNKT) cells are thymus-generated innate-like αß T cells that undergo terminal differentiation in the thymus. Such a developmental pathway differs from that of conventional αß T cells, which are generated in the thymus but complete their functional maturation in peripheral tissues. Multiple subsets of iNKT cells have been described, among which IL-17-producing iNKT cells are commonly referred to as NKT17 cells. IL-17 is considered a proinflammatory cytokine that can play both protective and pathogenic roles and has been implicated as a key regulatory factor in many disease settings. Akin to other iNKT subsets, NKT17 cells acquire their effector function during thymic development. However, the cellular mechanisms that drive NKT17 subset specification, and how iNKT cells in general acquire their effector function prior to antigen encounter, remain largely unknown. Considering that all iNKT cells express the canonical Vα14-Jα18 TCRα chain and all iNKT subsets display the same ligand specificity, i.e., glycolipid antigens in the context of the nonclassical MHC-I molecule CD1d, the conundrum is explaining how thymic NKT17 cell specification is determined. Mapping of the molecular circuitry of NKT17 cell differentiation, combined with the discovery of markers that identify NKT17 cells, has provided new insights into the developmental pathway of NKT17 cells. The current review aims to highlight recent advances in our understanding of thymic NKT17 cell development and to place these findings in the larger context of iNKT subset specification and differentiation.

Cytokine receptor γc effectuates the generation of proinflammatory innate CD8 T cells by non-classical MHC-I molecules.

Innate CD8 T cells correspond to a population of terminally differentiated effector T cells that phenotypically appear as antigen-experienced memory cells and functionally resemble proinflammatory CD8 T cells, expressing copious amounts of IFNγ. Innate CD8 T cells, however, are distinct from conventional effector-memory CD8 T cells as they acquire functional maturity during their generation in the thymus. Understanding the molecular mechanisms that drive their thymic development and differentiation is an intensely studied subject in T cell immunity, and here we identified the cytokine receptor γc as a critical mediator of innate CD8 T cell generation that promotes their selection even in the absence of classical MHC-I molecules. Consequently, overexpression of γc resulted in a dramatic increase of innate CD8 T cells in KbDb-deficient mice. We mapped its underlying mechanism to the expansion of IL-4-producing invariant NKT cells, so that it is the increased availability of intrathymic IL-4 which augments the selection of innate CD8 T cells. Collectively, these results unravel the selection of innate CD8 T cells being mediated by non-classical MHC-I molecules and being modulated by the abundance of the γc cytokine, IL-4.

The cytokine receptor DR3 identifies and promotes the activation of thymic NKT17 cells.

Invariant natural killer T (iNKT) cells correspond to a population of thymus-generated T cells with innate-like characteristics and effector functions. Among the various iNKT subsets, NKT17 is the only subset that produces the proinflammatory cytokine IL-17. But, how NKT17 cells acquire this ability and what would selectively trigger their activation remain incompletely understood. Here, we identified the cytokine receptor DR3 being specifically expressed on thymic NKT17 cells and mostly absent on other thymic iNKT subsets. Moreover, DR3 ligation promoted the in vivo activation of thymic NKT17 cells and provided costimulatory effects upon agonistic α-GalCer stimulation. Thus, we identified a specific surface marker for thymic NKT17 cells that triggers their activation and augments their effector functions both in vivo and in vitro. These findings provide new insights for deciphering the role and function of murine NKT17 cells and for understanding the development and activation mechanisms of iNKT cells in general.

The molecular basis and cellular effects of distinct CD103 expression on CD4 and CD8 T cells.

Integrin CD103 mediates the adhesion and tissue retention of T cells by binding to E-cadherin which is abundant on epithelial cells. Notably, CD103 is highly expressed on CD8 T cells but conspicuously absent on most CD4 T cells. The mechanism controlling such lineage-specific expression of CD103 remains unclear. Using a series of genetically engineered mouse models, here, we demonstrate that the regulatory mechanism of CD103 expression is distinct between CD4 and CD8 T cells, and that the transcription factor Runx3 plays an important but not an essential role in this process. We further found that the availability of integrin ß7 which heterodimerizes with CD103 was necessary but also constrained the surface expression of CD103. Notably, the forced surface expression of CD103 did not significantly alter the thymic development of conventional T cells but severely impaired the generation of MHC-II-restricted TCR transgenic T cells, revealing previously unappreciated aspects of CD103 in the selection and maturation of CD4 T cells. Unlike its effect on CD4 T cell development, however, CD103 overexpression did not significantly affect CD4 T cells in peripheral tissues. Moreover, the frequency and number of CD4 T cells in the small intestine epithelium did not increase even though E-cadherin is highly expressed in this tissue. Collectively, these results suggest that most mature CD4 T cells are refractory to the effects of CD103 expression, and that they presumably utilize CD103-independent pathways to control their tissue retention and residency.

Evaluation of the ex vivo Effects of Tamoxifen on Adipose-Derived Stem Cells: A Pilot Study.

Autologous fat grafting (AFG) is a safe and minimally invasive procedure to correct soft tissue defects. The benefit of AFG is attributed to adipose-derived stem cells (ASCs) in fat tissue graft. This technique is useful also in patients undergoing reconstructive surgery following quadrantectomy for breast cancer. However, these patients are frequently treated with tamoxifen. We evaluated the ex vivo effects of tamoxifen on ASCs to understand if cellular functions of ASCs are affected. We selected 24 female patients; 10 of which were breast cancer patients treated with quadrantectomy and tamoxifen. As control group, we selected 14 healthy female subjects (9 premenopausal and 5 menopausal). We found that tamoxifen has no effect on cellular proliferation, VEGF secretion or apoptosis of ASCs. The gene expression assessment demonstrated no impairment in differentiation capacity of ASCs. Our results showed that tamoxifen has no effect on cellular functions of ASCs for the first time in an ex vivo single-center study.